Educate your partner!
Talking about other men when she is in a relationship or on a date with you is a lack of dating skills.
It is a lack of tact.
You don’t need to hear that. The fantasies which go on in her mind are okay as long as she doesn’t picture them for you.
Tell her! Design a new boundary in your relationship.
Tell her until she gets it and shifts her attitude.
Going on a date with you is about you, the two of you, not her and someone else.
It is your right to establish a new boundary.
Tell her: “I would rather talk about something else. Is it okay with you?”
If you enjoy her love stories, it is different of course.
However, if this wakes up unwanted jealousy in you, tell her you don’t want to hear that.
Simple and direct!
When you are on a date, it is nice to feel valued.
It is about what you two have in common.
Educate her on that.
It is okay.
Repeat the message until she gets it.